| https://www.z1motorsports.com/forced-induction/z1-motorsports/z1-motorsports-300zx-upgraded-adjustable-wastegate-actuators-p-5550.html I had the same problem on my Sport 500s and replacing these fixed it.  My EBC is set at 16 psi and they hold fine...  From memory here - I think they need to be set to start cracking open 2-3 psi before where you want the boost to be and your boost controller will do the rest. 
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